58 METALLURGY OF IRON AND STEEL.
easier to reduce in the blast furnace, because at very low temperatures it is converted into magnetite,, losing a portion of its oxygen, in so doing, and thus opening pores throughout the mass. Moreover, during this reaction carbon deposition may occur, while it is well known that very little carbon is deposited with magnetite. Wiborgh shows that the degree of reduction is in proportion to the carbon deposition, the degree of reduction being the amount of reduced iron, expressed in per cent., of the total iron present. The results are tabulated herewith:
Carbon Degree of
Number of Tests. Deposited. Reduction.
6 0 to 1 70 to 82
6 1 to 2 83 to 86
4 2 to 3 85 to 86
2 4 to 6 90 to 93
In order to obtain a large proportion of deposited carbon, the temperature must be low and the ore porous. * In the case of Bilbao ore, the deposited carbon in one case reached 12.23 per cent. It is urged by Wiborgh that Fe00r plays an important part in the blast-furnace. He recognizes four oxides: Fe203, which he rates at 100 per cent, of oxidation; Fe304, rated at 88.9 per cent; FeO, rated at 66.7 per cent., and FeB07, intermediate between the ferrous and magnetic oxides, with a rating of 77.8 per cent, of oxidation. Experiments seemed to show that it was Fe007, and not FeO, which formed during the experiments, and that this oxide was directly reduced in accordance with the following reaction:
FeaOT+7 00=6 Fe+7 C02.
It is stipulated, however, that these .conditions obtain when there is neither hydrogen nor deposited carbon, as these two agents tend to the formation of ferrous oxide. It would seem rash to assume that a furnace would run without the formation of hydrogen or without the presence of deposited carbon, and it may be better to cling to the old theory that FeO is the next stage after the magnetic oxide.
Much remains to be discovered in this field. Thus Laudig states